Mouse anti-HM1.24 monoclonal antibody has been prepared using a human myeloma cell line KPC-32 as an immunogen (Goto, T. et al., Blood 84: 1922-1930, 1994). The HM1.24 antigen that is recognized by this antibody is a membrane protein having a molecular weight of 29 to 33 kDa that is overexpressed on the surface of myeloma cells. Furthermore, for normal cells its expression has been confirmed in immunoglobulin-producing B cells (plasma cells, lymphoplasmacitoide cells), but expression is rarely observed in the other cells and tissues (Goto T. et al., supra). However, nothing is known about HM1.24 antigen except its expression distribution and molecular weight.
According to the present invention, as a result of the cloning of genomic DNA encoding HM1.24 antigen, the determination of its nucleotide sequence and the deduced amino acid sequence, and further homology search, HM1.24 antigen was demonstrated to be a molecule identical with BST2 that is a surface antigen expressed on the stroma cells isolated from the bone marrow of patients with myeloma, and the bone marrow and the snynovial membrane of patients with rheumatoid arthritis. BST2 has been shown to have an ability of supporting the growth of pre-B cells and is thought to be involved in the pathology of rheumatoid arthritis, but its other physiological functions are not known (Ishikawa J. et al., Genomics 26: 527-534, 1995).
In the production of a useful gene product derived from an animal by means of genetic engineering, it often happens that the gene is not expressed, a gene product, protein, does not take a correct conformation, post-translational modification does not occur correctly and the like, when a microorganism host such as Escherichia coli, Bacillus subtilis, or yeast is used. In order to solve such problems, animal cells are often used as hosts, in which case, the selection of a promoter has a great impact on expression efficiency. Conventional, frequently used promoters for animal cells include SV40 promoter, cytomegalovirus promoter, actin promoter, and the like.